The present invention is directed to a process and catalyst for the regioselective production of para-substituted compounds, e.g. para-xylene. One aspect of the present invention includes a process wherein a feedstock which includes an aromatic hydrocarbon and a high efficiency, p-xylene selectivating agent are co-fed over a pre-selectivated catalytic molecular sieve.
Para-xylene is a very valuable commercial product useful in the production of polyester fibers. The catalytic production of para-xylene has received much attention in the scientific community and various methods for increasing catalyst para-selectivity have been described.
The synthesis of para-xylene is typically performed by methylation of toluene over a catalyst under conversion conditions. Examples are the reaction of toluene with methanol as described by Chen et al., J. Amer. Chem. Sec. 1979, 101, 6783, and toluene disproportionation, as described by Pines in "The Chemistry of Catalytic Hydrocarbon Conversions", Academic Press, New York, 1981, p. 72. Such methods typically result in the production of a mixture including para-xylene, ortho-xylene, and meta-xylene. Depending upon the para-selectivity of the catalyst and the reaction conditions, different percentages of para-xylene are obtained. The yield, i.e., the amount of feedstock actually converted to xylene, is also affected by the catalyst and the reaction conditions.
Previously known toluene methylation reactions typically provide many by-products such as those indicated in the following formula: